I should know this, but in what direction are DVD's read

[markrb]

I looked through and try to do a search, but the hits were huge using the terms I tried.

On a bought (not burned) DVD-9 where does the reading begin and end. Is a DVD read from the hub out or from the outside in?

I happen to have a DVD that is pretty badly scratched near the Hub, but so far there have been no errors. Basically the disc came loose in the box and I took three months to open it so it's way beyond the return period.

If it reads from the hub out then I think I will be fine since the first 2 of 4 episodes have shown no ill effects.


Thanks,
Mark

[dvd_maniac]

not sure which layer first on dual layer (dvd-9) discs though. As most episode dvd's are.

[ammck55]

Mark:

My terms weren't any better than yours, the last search returned 412,000 hits. I give up! :)

ammck55

[KpeX]

I am the googlemaster :sly:

Found this page: http://www.disktech.com.au/DVD/DVDInfo.htm

And this quote a few paragraphs down:

Dual layer discs can be constructed in two ways: Opposite track path and Parallel track path. In Parallel track path discs, the first layer is read from the inside of the disc to the outside, then the second layer is read in the same direction.

Opposite track path discs also have a Middle area, which bridges the point where the first layer ends and the second layer starts. The second layer is read from the outside of the disc to the inside

So that's not too much of an answer I guess, maybe someone who knows more than me could shed some light on which type is more commonly used.

Edit:

Maybe this helps a little more, from http://www.u-m-l.com/dvdconst.htm


Parallel Track: In general, parallel track path is used for dual-layer discs containing data and program files that are not used in any predefined order, such as DVD-ROMs. May be used for DVD Videos where the complete movie is recorded on Layer 1 and parallel plot lines or additional background relevant to specific scenes can be stored on Layer 1 adjacent to the scene involved.

Opposite Track: Used where a long movie will not fit completely on one layer. To prevent the movie finishing part 1 at the outer edge of the disc and then starting the next section at the middle of the disc on the second layer the second part of the movie starts at the outside edge of the disc and spirals in towards the middle of the disc.

So, since you said it's an episodic DVD, sounds like it could be parallel track, which would mean you're in good shape :).

[RoChess]

Also the 'cover me from a lawsuit' people, show this on the back of the DVD with 'There may be a slight pause in the transition of layers'.

Most DVDs (if not all) go from inner part to outside part, the drive actually slows down during this process. I can bore you with technical details involved, but in short it comes down to that the laser has to produce a constant stream of data. So since the inner rings contain less data, the DVD has to spin faster. Then when the laser graduates to the outer ring, the DVD slows down.

It would take too much time, to make the DVD spin faster, reposition the laser on the inner circle and start the 2nd layer, so that is why the 2nd layer goes opposite. But even this fast switch from layer, can cause a slight delay, hence the 'cover me from a lawsuit' notice on the back of the DVD cover.

Even if it's not a long movie that didn't fit on one layer, it is mostly done that way. But when you for example switch layers on a DVD that has 4 episodes of a TV show on it, the switch is most likely to occur between episodes, so it would never be noticable.

But it's all up to the person who actually mastered the DVD, and eventho it is not common, some might use the parallel method.